1. Field of the Invention
The present invention relates to a thermochromic opaque/transparent composition, a laminate member employing the same, and a three-dimensional member employing said laminate member and capable of concealing and revealing the interior. More particularly, the present invention relates to a thermochromic opaque/transparent composition of which transparency/opacity reversibly varies with certain hysteresis, together with color change, in response to temperature variation, a laminate member employing said composition, and a three-dimensional member employing said laminate member and capable of concealing and revealing the interior.
2. Related Background Art
In the field of thermochromic material capable of reversible color change in response to temperature variation, there is already known, as disclosed in the Japanese Patent Publication Nos. 51-44706 and 51-44707, a material effecting a color-generating reaction between an electron donating compound and a phenolic compound in the presence of a compound having an alcoholic hydroxyl radical.
Also as an application of such thermochromic material, the Japanese Patent Publication No. 51-35216 discloses a thermoplastic polymer composition comprising (a) an electron donating color-developing compound, (b) a compound having a phenolic hydroxyl radical, (c) a compound selected from alcohols, esters, ketones and ethers, and (d) thermoplastic polymer.
Such prior technologies are featured by reversible color change. Although there is described that a variation in the transparency/opacity occurs together with the color change, the mixture of the components (a), (b) and (c) in the above-mentioned invention, simply added in the thermoplastic resinous polymer has been associated with drawbacks of significant loss in the developed color density and in the sensitivity of color change due to the polar effect of said thermoplastic polymer. Also in the thermoplastic polymer composition of the above-mentioned invention, the thermoplastic materials consisting of the components (a), (b) and (c) are often liquidous already at the room temperature or at the color change, whereby there is often encountered so-called bleeding phenomenon in which one of said three components is separated on the resin surface in the initial stage after the preparation of the thermoplastic polymer composition, or after repeated color changes thereof. For these reasons it has been practically difficult to stably maintain the aforementioned three components in the thermoplastic polymer for a prolonged period, with satisfactory color changes in repeated temperature variations.
The thermochromic material of the above-explained three-component system, capable of showing color change only when three components are present together, is usually incorporated in microcapsules and protected by the microcapsule wall. As a result, said material is rendered stable against the external chemical or thermal actions and applicable to various purposes.
However, said three components are converted into a kind of solid pigment by said microencapsulation, and, when such microencapsulated pigment is dispersed in vehicle resin, transparency thereof is significantly lowered by the surfacial light scattering specific to the pigment even if the vehicle resin itself is transparent. Such vehicle layer is capable of concealing and revealing an underlying picture when it is practically adhered to said vehicle layer, but such underlying picture cannot be viewed through the microcapsule-containing vehicle layer if said picture is separated therefrom by a certain distance.
Thus, in case the conventional three-component thermochromic material is directly incorporated in the resin without microencapsulation, it has been practically difficult to obtain a composition which clearly reveals the interior of a three-dimensional object, with satisfactory color change, in response to temperature variation in stable manner.
On the other hand, a composition capable of causing a change in transparency/opacity is disclosed in the U.S. Pat. No. 4,268,413. Said composition is composed of an organic substance and an optically transparent polymer material and has temperature-dependent light absorption, in which the refractive index of said organic substance coincides with that of the polymer material according to temperature variation, thereby reversibly inducing a change in transparence/opacity.
The above-mentioned composition reversibly repeats the change between transparent and opaque states according to temperature variation. Basically the transparent state is colorless, and the opaque state is white. It is basically unable to show a change in the hue, for example between blue and pink. Also said optically transparent polymer material is determined by the relation with the organic substance in refractive indexes thereof, namely by the physical factor only, and does not involve a change in the hue.